1. Field of the Invention
The invention relates generally to the manufacture of composite cellulosic materials. More particularly, the invention relates to methods for cleaning apparatus used in the consolidation of composite cellulosic materials.
2. Brief Description of Related Technology
Composite cellulosic materials can advantageously be used in the manufacture of many different products. Composite cellulosic materials can be molded to have various shapes and sizes and to have various design and structural features which may or may not have been available with products made from natural wood or other materials. Methods for producing manmade cellulosic composites are disclosed, for example, in U.S. Pat. No. 5,367,040 (Nov. 22, 1994) to Teodorczyk and U.S. Pat. No. 4,514,532 (Apr. 30, 1985) to Hsu et al. The disclosures of these patents are hereby incorporated herein by reference.
A variety of types of cellulosic (e.g., wood) composite materials exist, including flat or contoured boards of pressed cellulosic material and/or boards of bonded cellulosic sheets. Examples of types of useful man-made boards can be referred to by the following terms: (a) fiberboards, such as hardboard, softboard, and medium density fiberboard and (b) chipboards, such as particleboard and oriented strandboard. Composites of these boards (i.e., articles comprising two or more of these materials) can also be useful.
Many different methods of manufacturing these cellulosic composites are known in the art. Methods for manufacturing fiberboard include (a) wet felted/wet pressed or "wet" processes, (b) dry felted/dry pressed or "dry" processes, and (c) wet felted/dry pressed or "wet-dry" processes. Synthetic resins, such as phenolformaldehyde resins, are often used as binders in these processes.
Generally, in a wet process, cellulosic fillers are blended in a vessel with large amounts of water to form a slurry. Useful cellulosic materials include, for example, woody material that is subjected to fiberization to form wood fibers. The slurry preferably has sufficient water content to suspend a majority of the wood fibers. The slurry is deposited along with a binder material, such as resin binder, onto a water-pervious support member, such as a fine screen or a Fourdrinier wire, where much of the water is removed to leave a wet mat of cellulosic material having, for example, a moisture content of about 50 weight percent. The wet mat is then consolidated under heat and pressure to form the cellulosic composite.
A wet-dry forming process can also be used to produce cellulosic composite materials. Preferably, a wet-dry process begins by blending cellulosic or wood fiber material in a vessel with a large amount of water. This slurry is then blended with a binder material. The blend is then deposited onto a water-pervious support member, where a large percentage of the water is removed, thereby leaving a wet mat of cellulosic material having a water content of about 40 weight percent to about 60 weight percent, for example. This wet mat is then transferred to a zone where much of the remaining water is removed by evaporation to form a dried mat having a moisture content of less than about ten weight percent. The dried mat is then consolidated under heat and pressure to form the cellulosic composite.
In a dry-felted process, the cellulosic filler is generally conveyed in a gaseous stream or by mechanical means. Cellulosic fibers can be first coated with a binder material, for example in a blowline blending procedure. The resin-coated fibers can then be randomly formed into a dry mat by air blowing the fibers onto a support member. The dry mat is then consolidated under heat and pressure to form the cellulosic composite.
Processes such as those described above, for example, can be used to manufacture a product having any desired shape depending on the intended use of the product. As mentioned above, the mat which is formed by a felting process (such as one of the felting processes described above) is typically placed in a pressing apparatus. The pressing apparatus typically includes a pair of pressing dies, often referred to as a die set. The mat is subjected to elevated temperatures and pressures in the pressing apparatus, so as to cure the binder material and compress the mat into an integral consolidated structure.
One disadvantage of the above-described methods is that undesirable by-products of the pressing operation tend to build up on the surfaces of the die sets. Each of the above-described methods can result in the formation of such undesirable materials. These undesirable materials can be in the form of a film that contains carbon and other materials. Such a film is commonly referred to as a "carbon film" or "carbonaceous film." The carbon film is undesirable, for example, because it may interfere with the pressing operation and/or damage the final product. For example, when this build-up problem becomes severe, flakes of the carbon film can come off of the dies and be pressed onto or through the surface of the production mat which is being pressed. Such an occurrence can create a downgraded or unusable product. Such a film can also damage the die surfaces themselves.
In the past, because the carbon film is difficult to remove from the die surfaces, this problem has typically been overcome by removing the dies from the pressing apparatus for cleaning. The need to remove the dies from the pressing apparatus is generally undesirable due to the extra cost, complication, and time which is required for the operation. Such an operation can create a loss of production time of approximately six to eight hours. Other attempts to use in-press cleaning of dies, for example, those processes using caustic soda, sticky resins, water, or other chemicals can be dangerous and/or not effective.
Therefore, it is desirable to provide a method for satisfactorily cleaning die sets of pressing apparatus. It is also desirable provide an effective method for cleaning die sets without the need to remove the dies from the pressing apparatus. It is further desirable that such methods are not dangerous to the user and cannot cause damage to the products which are manufactured in the pressing apparatus.